Most of the world production of carbon blacks, especially the furnace carbon blacks required for the filling of heavy-duty rubber articles, are produced according to the furnace carbon black or oven carbon black method. Basically, in this method a hot rotating mass of combustion gases is formed by the combustion of gaseous or liquid fuels, usually natural gas at the present time. Tubular flow reactors are generally used which are usually horizontally oriented and covered in a fire-resistant manner. With tangential introduction of air to create a hot rotating mass, a liquid hydrocarbon with a highly aromatic composition, e.g. a carbochemical or petrochemical oil, is injected, usually axially, by means of an oil injector extending into the reactor zone with a single-component or two-component atomizer.
The introduced hydrocarbon is essentially cracked at the high temperatures of approximately 1400.degree.-1800.degree. C. into carbon (carbon black) and hydrogen. A few known methods generate combustion waste gases in a separate precombustion chamber located in front or ahead of the actual reaction zone wherein the carbon black is formed. In these methods, combustion air which has usually been preheated in heat exchangers with the reaction mixture leaving the reactor to 300.degree.-600.degree. C. or higher is tangentially blown by a rotary piston or turboblower into the combustion chamber through one or several (symmetrically arranged in the latter instance) conduit openings positioned on the circumference of the combustion chamber in such a manner that a swirling flow is created.
A fuel such as burnable gas, e.g. from a burner/injector combination as is described in DE-PS 24 10 565, is added into this intentionally induced swirling flow so that a mass of hot, rotating gases is created which moves forward in a helical manner, confined by the inner walls of the reaction tube, to the reaction zone where the gas, now burned-out to a great extent, is charged with the carbon black raw material by spraying in very fine particles.
It is considered to be an important condition for the production of furnace carbon blacks that the mixing of the carbon black raw material into the hot combustion gases should occur rapidly. An effective means of inducing a rapid and intensive mixing can be to allow the rotating hot gaseous mass to pass through a narrow area in the reactor after, during or shortly before the injection of the carbon black raw material. This narrow area consists of a constriction of the inner reactor zone contour achieved by means of suitable built-in elements such as, e.g. a so-called restrictor ring or by other built-in elements whose contours can be, e.g. conical, Laval-shaped, Venturi-shaped or with some other shape.
The swirling flow of hot combustion gases can also be created in some other manner. One possibility is to add the fuel from the periphery of a combustion chamber located in front, e.g. by means of introducing it into tangentially supplied combustion air.
Another possibility is described in DE-AS 15 92 852 which provides either for injecting the fuel in an axial direction into one end of a longitudinally extended cylindrical combustion chamber positioned laterally and tangentially at the upstream end of a Venturi reactor, or introducing the air tangentially into the same end of the combustion chamber and then introducing the hot combustion gases created tangentially into the end of the reactor chamber located upstream and designed as cylindrical section.
Another possibility for introducing combustion air and fuel makes no use of a separate combustion chamber and mixes combustion air and fuel in one or several conduits which connect in an essentially tangential position in the vicinity of the front of the reactor in round or slotlike feed conduits into the reactor. Gas lances are movably located in the conduits in order to produce the air/burnable gas mixture. If a liquid fuel is to be used instead of burnable gas, the gas lances are replaced by suitable single-component or two-component atomizers.
However, combustion air and fuel can also be introduced by separate conduits tangentially positioned on the circumference of the front part of the carbon black oven, whereby they are not mixed and burned until they are within the swirling flow formed in the furnace.
In all these oven designs, a helically rotating mass of hot combustion products is produced in the front part of the reactor into which mass the carbon black raw material can be sprayed after a certain distance, optionally in front of, directly into, or a short distance after, the location of a narrow area in the reaction zone. This is referred to as the zone of constriction. The premixing of fuel and combustion air before their entrance into the reactor makes it possible to design the latter more compactly. Thus, all previously discussed designs for furnace carbon reactors have the goal of creating a strong swirling action of the gaseous heating medium for the cracking reaction, whereby the swirling gaseous mass is affected but not eliminated if a constriction is used. The effect of the swirling motion of the gases is considered to be that the small droplets of liquid injected into the hot combustion gases during the injection of the carbon black raw material are divided or sheared into still small particles by means of spontaneous change of direction due to the turbulance. Direct proportionality with the swirling intensity was assumed for the shearing forces created thereby.
The generation of rotating gaseous masses according to prior known methods requires a considerable expenditure of mechanical energy. Since a rotating eddy of hot gas does not rotate quite symmetrically under practical conditions but rather wobbles somewhat and also since an absolute rotational symmetry of the injected oil in relation to the eye of the vortex cannot be achieved, droplets of oil tend to deposit on the reactor wall. That is, on the jacketing in walled reactors, the oil droplets form and carbonize there. This deposition tends to loosen parts of the wall and also brings about a change of the carbon black oil/hot gas ratio. This can cause the iodine number to rise; also, the quality parameters set for the desired carbon black can be changed, since oil is removed from the formation of carbon black. Thus, deposited coke grows unsymmetrically on parts of the oven interior for the reasons cited above, and as a result of chemical and mechanical actions causes damage to the oven walls and contaminates the product by means of loosened particles.
In view thereof, there was a great need to find a method with which the entire range of specifications at least of the activated carbon blacks can be achieved and in which the cited problems rarely or no longer occur.
As a result of the invention, a new oven design was developed as well as a method which can be carried out to produce furnace carbon black, which method in the light of the flow conditions prevailing in the reactor proceeds in a new way and solves the described problems to a great extent.